1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to a driving method for local dimming of an LCD device, which accurately detects the total light intensity of each pixel simply by changing light intensity data, in spite of a changed optical profile, and an apparatus using the same.
2. Discussion of the Related Art
Recently, flat panel displays have been popular as video displays, such as LCDs, Plasma Display Panels (PDPs), Organic Light Emitting Diodes (OLEDs), etc.
An LCD device includes a liquid crystal panel for displaying an image on a pixel matrix relying on the electrical and optical characteristics of liquid crystals that exhibit anisotropy in dielectric constant and refractive index, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light onto the liquid crystal panel. The gray scale of each pixel is adjusted by controlling the transmittance of light that passes from the backlight unit through the liquid crystal panel and polarizers through changing the orientation of liquid crystals according to a data signal.
In the LCD device, the luminance of each pixel is determined by the product between the luminance of the backlight unit and the light transmittance of liquid crystals that depends on data. The LCD device employs backlight dimming for the purposes of increasing a contrast ratio and reducing power consumption. Backlight dimming is a technique that controls backlight luminance and compensates data by analyzing an input image and adjusting a dimming value based on the analysis. For example, a backlight dimming method intended for reducing power consumption reduces the backlight luminance by decreasing the dimming value and increases the luminance through data compensation. Thus the power consumption of the backlight unit is reduced.
A Light Emitting Diode (LED) backlight unit using LEDs as light source has recently been used. The LEDs boast of high luminance and low power consumption, compared to conventional lamps. Because the LED backlight unit allow for location-based control, they may be driven by local dimming. According to the local dimming technology, the LED backlight unit is divided into a plurality of light emitting blocks and luminance is controlled on a bock-by-block basis. Local dimming may further increase the contrast ratio and decrease the power consumption since the backlight unit and the liquid crystal panel are divided into a plurality of blocks, local dimming values are decided by analyzing data on a block basis, and data is compensated based on the local dimming values.
However, the local dimming technique according to the related art controls the luminance of backlight unit on a block basis by dividing the backlight unit into a plurality of light emitting blocks, thus decreasing a total luminance, compared to global dimming in which the entire luminance of lamp backlight unit is controlled. In this context, the decreased backlight luminance is compensated for by compensating input data simultaneously with local dimming. For this purpose, the intensity of light that reaches each pixel is analyzed based on an optical profile specifying light intensities of a light source among the backlight unit according to distances from the light source, and a gain value is calculated for data compensation using the analyzed light intensity of the pixel. Therefore, the light intensity of each pixel should be accurately calculated to accurately compensate the luminance of data.
In a local dimming method according to the related art, the intensity of light that reaches each pixel from a light source is calculated using functions such as a Gaussian function, a Butterworth function, etc. with similar characteristics to an optical profile, as illustrated in FIG. 1. Although when backlight unit is illuminated with the same luminance across the entire area of a screen, the intensities of light reaching pixels should be identical, the light intensity is not equal at each pixel with respect to the same luminance of the backlight unit in case of the functions of the related art. The difference between compensation data for the same data under the same luminance of backlight unit may degrade image quality. Moreover, in the case where local dimming is performed by an algorithm that analyzes light intensity using the functions of the related art, if a change occurs to an optical profile according to the shape and type of a light source, a new algorithm should be employed.